(CNN) -- Former world MotoGP champion Casey Stoner has confirmed he will miss the next three races in the series in a bid to cure the mystery illness which has hindered his season.

2007 champion Stoner has been suffering from a mystery illness which has hindered his MotoGP season.

Australian Stoner, the 2007 champion, has been suffering from severe fatigue since the Grand Prix of Catalunya in June -- and was a dismal 14th in the British round at Donington in his last race.

Doctors have now advised the 23-year-old Marlboro Ducati rider, who lies third in the standings behind Fiat Yamaha duo Valentino Rossi and Jorge Lorenzo, to sit out the next three rounds beginning at the Czech MotoGP in Brno this Sunday.

Stoner told the official MotoGP Web site: "After five extremely difficult races due to my health, I have returned to Australia to visit the sports doctors who have looked after me for many years.

"We have taken the difficult decision not to contest the next three rounds of the championship, to allow my body time to recover from the recent stress.

"The doctors believe that during the Barcelona race I was suffering from a virus, and that I subsequently pushed my body too hard, leading to problems that have caused my fatigue since then.

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"The doctors are continuing with many tests to try to understand these problems and make sure it does not happen again. I have spoken with Ducati and thank them for their understanding at this time.

"I feel very sorry for the factory, my team, my sponsors and the fans and I am also disappointed because the bike in the last few races has been very competitive. I will be doing everything possible to come back at full strength for Portugal."

His place, alongside Nicky Hayden in the factory Ducati side, will be taken by Finnish rider Mika Kallio, who has been competing for the Pramac Ducati team.

Stoner's next appearance should be at the Portuguese Grand Prix which will be at Estoril on October 4.